1. Field of the Invention
The present invention relates to an internal combustion engine inner-cylinder pressure estimation apparatus and more particularly to an internal combustion engine inner-cylinder pressure estimation apparatus that can simulate the present inner-cylinder pressure in real time.
2. Description of the Related Art
Because of the recent environmental and energy problems, an internal combustion engine control apparatus is required to further improve gasoline mileage. For this requirement, to date, the ignition timing has been optimized so as to approach the MBT (Minimum Advance for Best Torque), the pumping loss and the internal EGR amount have been optimized by a VVT (Variable Valve Timing) mechanism, and the Atkinson cycle has been achieved through intake-valve delayed closing utilizing the VVT mechanism; furthermore, the pumping loss and the external EGR amount have been optimized also by an EGR (Exhaust Gas Recirculation) mechanism.
As described above, in order to appropriately control a great number of control parameters, the inner-cylinder pressure is measured and the optimum operation condition is studied so that gasoline mileage is improved; however, because in order to implement the optimization, a massive amount of data is required originally, the number of measurement points are decreased by use of a DoE (Design of Experiments) or the like, and statistic modeling through a MBC (Model-Based Calibration), numerical optimization, or the like is also utilized so that the number of maps required for the control is decreased.
The foregoing method is for the optimization of control parameters that utilizes a statistic model; however, there has also been studied optimization of the ignition timing or the like in which instead of a statistic model, a physical model is utilized. In other words, through a physical model, the inner-cylinder intake air amount and the EGR amount are calculated from the control amounts for the VVT and the EGR and the outputs of various kinds of sensors, and then based on the calculated intake air amount, the calculated EGR amount, and the calculated ignition timing, a combustion simulation based on the physical model is implemented and then the inner-cylinder pressure is estimated, so that even under an operation condition in which the inner-cylinder pressure is not measured, the control amounts of the VVT, the ECR, the ignition timing at a time when the gasoline mileage is best are calculated so that the respective control parameters are optimized.
Moreover, due to the performance improvement of a microcomputer utilized as the control apparatus of an internal combustion engine, it has also been studied that a combustion simulation is implemented in real time while the internal combustion engine is controlled, so that the estimation of the inner-cylinder pressure and the optimization of various kinds control amounts are performed.
As an example of combustion model, among physical models, that is utilized in a combustion simulation in particular, for example, in a method disclosed in Japanese Patent Application Laid-Open No. 2004-293541 (Patent Document 1), a combustion physical model is established by estimating the flame propagation based on a flame growth through turbulent combustion and a flame growth through laminar combustion. In addition, for example, in a method disclosed in Japanese Patent Application Laid-Open No. 2009-332658 (Patent Document 2), a main combustion period is calculated based on a laminar combustion velocity and then an MBT ignition timing is calculated based on the main combustion period. As an approach that is different from such combustion simulations close to a combustion physical model, for example, in a method disclosed in Japanese Patent Application Laid-Open No. 2008-215209 (Patent Document 3), simulation of a heat generation rate is implemented by use of a Wiebe function for approximating a fuel ratio.